HR: 1340h
AN: S13D-1086 [Abstracts]
TI: Scaling Relationship Among Source Parameters of Microearthquake," From Near Source Observation in a
Deep Mine
AU: Hiramatsu, Y
EM: yoshizo@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kakuma, Kanazawa, 920-1192
Japan
AU: * Yoshimura, M
EM: yoshimura@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kakuma, Kanazawa, 920-1192
Japan
AU: Furumoto, M
EM: furumoto@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kakuma, Kanazawa, 920-1192
Japan
AB:
Scaling relationships among various source parameters are important clues to understand the source process. In particular the
relationship between the corner frequency, $f_C$, and the seismic moment, $M_O$, has been investigated by many researchers.
Aki(1967) investigated $f_C$ and $M_O$ using the spectra of seismic waves and reported that these parameters obeyed a
relationship of $M_O \propto f_C^{-3}$. For small earthquakes, the breakdown of this relationship was often reported. On the
other hand, no breakdown of the relationship for microearthquakes has been reported from high quality observation at deep
boreholes and in a deep gold mine. We report here these scaling relationships using waveform of microearthquakes observed at
the distance range of 15m to 1km.
We installed nine tri-axial borehole accelerometers within 200 m along a haulage tunnel 2650m deep in Mponeng mine in South
Africa from February to December in 1996. More than 25 thousand seismic events were recorded with a sampling frequency of 15
kHz and a dynamic range of 120 dB. The recording system has flat response up to 2 KHz. Among those events, we select 378
events with high S/N. We locate hypocenters assuming infinite medium with the P-wave velocity 5.5 km/s and the S-wave
velocity 3.2 km/s. We calculate the green function using the discrete wavenumber integral method into account the effect of
anelasticity by Takeo (1985) and determine the seismic moment and the mechanism using moment tensor inversion. We apply the
omega square model by Brune (1970) to determine the corner frequency and the stress drop. Minimizing L2 norm between the
observed spectra of P and S waves and the synthetic ones give the optimum source parameters.
The earthquakes analyzed in this study show the constant stress drop of 0.4$\sim$8MPa in the ranges of 40$
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting